Electron tube



Nov. 19, 1935. F BELW 2,021,764

ELECTRQN TUBE Filed Feb. 8, 1953 Patented Nov. 19, 1935 UNITED STATES 2,021,764 ELEcTRoN TUBE Fritz Below, Rahnitz-Hellerau, near Dresden,

Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a. company Application February 8, 1933, Serial No. 655,792 In Germany February 15, 1932 3 Claims. (Cl. 179-171) Low frequency amplifiers, especially those containing repeating resistances, are to some extent able to amplify high frequency too. High frequency receivers fitted with such amplifiers are 5 therefore energized by high frequency couplings that arise between the loudspeaker line and antenna line, and are in this Way caused to perform natural oscillations.

In order to avoid this, in most-cases filter sections for the high frequency, consisting of high frequency chokes or ohmic resistances and condensers, have been interposed between the detector tube and low frequency amplifier and frequently between the low frequency stages tool.

l5 Further, in many cases the practice has been to connect condensers in parallel to the anode circuit of the detector tube and low frequency tubes.

The invention deals with the electron tubes used in this connection, and more particularly 20 with electron tubes having a screening grid.

Such screening grid tubes have very great internal resistances and therefore require high external resistances to be provided. The capacity that serves for deriving the high frequency can 25 consequently be detrimental inasmuch as it acts to weaken the high-pitched notes to a marked degree.

According to the invention, the tendency of the 10W frequency amplifiers to amplify high fre- 30 quency too is decreased by a novel arrangement of high frequency chokes. The invention mainly consists in disposing the choking device in the leading-in wire of the screening grid, i. e. connecting this grid to the source of current by the 35 choking device. Such arrangement may be adopted in the construction of the detector tube or of one of the low frequency amplifying tubes, to which the terminal screening grid tube belongs, or in the construction of a number of such 40 tubes.

The invention Will be understood from the following description and be particularly pointed out in the appended claims, reference being had to the accompanying drawing in which an example 45 of an electron tube constructed in accordance with the invention is shown diagrammatically.

In this drawing, +A, -A denotes a source of direct current, B the anode, E the screening grid of the anode, F'the cathode, H the cathode heater,

50 G the grid of the tube, D a choke, C a condenser. By W two resistances are indicated.

The parts E, D, C, F, W are connected with each other in a manner that will appear from the drawing. 55 The resistances W serve in a well-known manner to decrease the tension applied to the grid E, this tension being produced by the current source -l-A, A.

The condenser C is to prevent the resistances W from causing the tension of the grid E to fluc- 6 tuate in the rhythm of the low frequency and thus likewise impairing the loW frequency amplification.

The choke D should present only a very small resistance to the low or audio frequencies, in orl0 der not to impair the amplification imparted to these frequencies. The choke Wire is therefore preferably of copper. With regard to the high frequencies, that is, frequencies above the audio frequencies, however, the resistance of the choke D should be as great as possible. The tension. of the grid E will then vary in a similar manner to the anode tension, namely in the rhythm of the high frequencies.

In this way the amplification factor of the tube is decreased as regards high frequency, so that the tube will act like a triode as far as high frequency is concerned.

It has been ascertained that by this invention the detrimental high frequency tensions in the loudspeaker line or other telephone line can be diminished to such an extent that natural oscillations of the receiver do not occur. Equally, noises due to cutting in the back coupling are now avoided.

The invention is adapted for use with resistance coupling as well as other coupling means.

What is claimed is: l

1. The combination of an audio frequency amplifier tube having electrodes including a cathode, an anode and a screening grid for the anode,

a source of constant current having the negative terminal thereof connected to the cathode, a potentiometer connected across said source, a connection from a point on said potentiometer to said screening grid, a choke coil of low impedance to audio frequencies and of high impedance to super-audio frequencies in said connection, and

a condenser connected in parallel Awith the portion of said potentiometer between said point and the negative terminal of said source.

2. The combination vof an audio frequency ampliiier tube having electrodes including a cathode, an anode, and a screening grid for the anode,

a source of constant current, a choke coil over which current from said source is connected to said screening grid, and a condenser connected between said cathode and that end of said choke coil which is connected to said source thereby to provide from said cathode through said condenser and said choke coil to said screening grid a, path of 10W impedance to frequencies within the audio range and high impedance to frequencies above said range.

3. The combination of an audio frequency amplier tube having electrodes including a cathode, an anode and a screening grid for the anode, a. source of positive potential for said screening grid, and a. path from said cathode to said screening grid including an inductive coil having high impedance for frequencies above the audio range and low impedance for frequencies within the audio range whereby the amplification factor of the tube is reduced for frequencies above said audio range Whilst being maintained for frequencies Within said audio range.

FRITZ BELOW. 

